Double clicking on a probe on a robot in IM returns the following error:
Unable to reach controller, node: (nodename) error message: communication error
Release : 20.3
Component : UIM - REBOOT
This is almost always going to be a network/firewall issue of sorts.
Install a telnet client and perform the following from a command prompt on the hub:
telnet <ip address of the problem robot> 48000
When initiated on Windows the command window should go blank. If the message is connecting, and ultimately there is a failure, the networking team will need to be engaged to understand what is blocking this communication between the hub and the robot.